[Desmoid tumor of the abdominal wall preoperatively suspected as urachal tumor: a case report].

A case of desmoid tumor of the abdominal wall which was preoperatively suspected as urachal tumor is presented. The patient was a 56-year-old man, who was referred to our clinic for further examination of the mass detected incidentally in the ventral region of the urinary bladder by computed tomography. Ultrasonography showed that the mass had a heterogenous and hypoechogenic content. An urachal tumor was suspected and surgery was performed to remove the tumor. During the operation we found that the tumor was completely separated from the urinary bladder and that it had originated from the left rectus abdominal muscle. The pathological diagnosis was desmoid tumor of the abdominal wall. Since urachal tumor has no characteristic findings on the imaging examinations, it is difficult to differentiate desmoid tumor of the lower abdominal wall from urachal tumor, preoperatively.